Totally different take on a FPS with a sci-fi storyline and an undersea world that's falling apart. Not to mention awesome powers, graphics and sound effects. The level of polish on this game is fantastic compared to most shooters. The way that fire, water and distortions relating to water and ice are integrated into the story and interact with physical objects (including you), are particularly impressive. But the best thing is the story. Usually I only like multi-player mode in FPS, but in this game I think I'll like the Single Player mode much better because of said story. And it's really challenging even on "medium mode".
Big Daddy says, get yourself to the App Store and buy some Bioshock 2.